Tool assembly for repairing and in particular grinding a tap seat

ABSTRACT

This relates to a tool assembly for repairing, and in particular, grinding a tap seat. The tool assembly includes a cutting tool carrier shaft and the primary features of the device are concerned with the guiding of the tool carrier shaft so that the tool carrier shaft is axially fixed without play in a guide while being free to rotate to effect the necessary machining operation.

In the present applicant's French patent application No. 77 11989 filedon Apr. 21, 1977 and the first certificate of addition No. 78 06274thereto dated Mar. 6, 1978, the present applicant described a toolassembly for in situ repair of a tap seat.

The tap assembly described therein comprises an adapter, a guide carriedby the adapter, a tool carrier shaft with a rotary drive means, theabove-mentioned adapter having an end portion comprising a screwthreadwhich is complementary to that of the tap body and a support shouldersuch that the end portion constitutes a replica of the tap body.

In a particular embodiment which forms the subject-matter of theabove-mentioned first certificate of addition, which is intended inparticular for restoring a tap seat by grinding thereof, the guide isassociated by screwing with a casing member which extends the endportion, and it comprises a bottom portion forming a thrust bearing forthe tool carrier shaft, whereby the thrust bearing is adapted to fix theaxial position of the tool carrier shaft with respect to the guide andto determine the forward feed movement of the tool by rotation on thecasing member which remains fixed.

Simultaneously with this axial fixing action, the tool carrier shaft isguided radially so that it cannot perform radial oscillatory movementswhich would have inevitable repercussions on the tool and moreover onthe machining operation effected. For this purpose, it has been proposedthat the tool carrier shaft may be radially guided at the position ofthe end portion, that is to say, over a portion of the tool carriershaft which is adjacent the tool; more briefly, in such an embodiment,the tool carrier shaft is held at two spaced points, one being an axialfixing means disposed in the vicinity of the rotary drive means and theother being a radial guide means disposed in the end portion which isconstructed for that purpose.

The present invention is generally concerned with guiding the toolcarrier shaft; in an alternative form of the above-mentionedarrangements, the present invention seeks to incorporate in the toolassembly, guide means which are distributed over virtually the entirelength of the tool carrier shaft in combination with axial fixing means,said means being capable not only of providing for a further improvedaxial and radial guiding action in respect of the tool carrier shaft,with tight production tolerances, but also making the device moreflexible in operation.

In accordance with the present invention, the tool assembly ischaracterised in that, for axial fixing of the tool carrier shaft, thethrust bearing comprises a double-acting ball-bearing thrust means whoseouter race is fixed with respect to the guide while the inner race isfixed with respect to the tool carrier shaft which is arranged for thatpurpose.

The tool carrier shaft is thus axially fixed without play in the guide,while being perfectly free to rotate.

In conjunction with the above-mentioned axial fixing action in respectof the tool carrier shaft, the tool assembly according to the presentapplication is characterized in that the radial guide means comprise atleast one anti-friction ring which is broached after being force-fittedinto one and/or the other of the end portion-casing member components,said ring being adjusted with close production tolerances of the orderof a hundredth of a millimeter, permitting free rotation of the toolcarrier shaft without play.

In practice, two rings such as that discussed above are providedrespectively in the end portion and in the casing member; they arebroached jointly after being force-fitted into said components in such away that their respective axes are in perfect alignment.

This results in such an arrangement that, at a terminal portion, thetool carrier shaft is adjacent the rotary drive means, being fixedaxially with respect to the guide, without play, while in combinationtherewith the radial guide action is provided in two regions,respectively an intermediate region and a terminal region, plus a regionformed by the ball-bearing type thrust means.

In accordance with another feature, the races of the ball-bearing thrustmeans comprise roller tracks with deep grooves which enclose the ballsover at least half their great circular, thereby permitting such aball-bearing thrust means to resist substantial axial thrust forceswhich may occur.

As regards the end portion, it is known that there are on the marketmany types of taps wherein the systems of assembling the tap head to thebody, by a female thread or nut, are of different diameters and pitches,so that, in order to be capable of dealing with the range of diametersand pitches used, the above-discussed tool assembly must be suppliedwith as many end portions as there are types of tap body.

Another object of the present application seeks to limit the number ofend portions by an arrangement thereof, the end portions being adaptedto form an approximately satisfactory replica in respect of at least twodifferent types of tap body nuts or female threads.

For this purpose, the end portion having a screwthread which iscomplementary to that of the body and a support shoulder on the terminalface of said body, is characterised by:

an end portion screwthread comprising at least one turn with a pitchwhich is intermediate the pitches of two different types of a range oftypes of tap body nuts;

a thread bottom diameter adapted to the smallest of the thread crestdiameters of the two types of nut;

and a reduced-thickness thread profile which provides with respect toone or other of the nut profiles of the two types, a supplementaryclearance which is at least equal to half the difference between the twopitches.

Practical tests show that with the same end portion of theabove-described configuration, it is certain that there is at least onescrew-nut contact region when the support shoulder of the end portioncomes into abutment against the terminal face of the tap body, and thatin this way it will be possible to hold the tool satisfactorily on atleast two different types of tap body wherein the screwthreads are ofvery close diameters but of different pitches.

As an end portion can be fitted to at least two different types of tapbody, it will be seen that the main advantage resulting from such anarrangement is a substantial reduction in the number of end portionswhich were previously required.

Another advantage of the supplementary clearance formed by theconfiguration of the profile of the screwthread turns is the resultingfacility for producing the end portion by moulding, in particular in asuitable plastics material.

In accordance with a particular embodiment, the various components ofthe tool assembly, namely the adapter, the end portion, the guide and adrive wheel associated with the tool carrier shaft are advantageouslyformed by moulding a suitable plastics material.

In accordance with another embodiment, the adapter with its screwthreadas defined above form an integral component.

A tool assembly of this kind, comprising components of plasticsmaterial, enjoys the advantage that it can be produced at highproduction rates; in addition, the number of components involved inproduction of the tool assembly is limited in particular by virtue ofthe adapter with its end portion comprising a single component.

In combination with the above-described arrangements, the inventionprovides a cutting tool which is specific to the machining operation tobe performed, the tool being characterised in that it comprises aterminal engagement face with radial cutting teeth which areadvantageously limited to three, and a shank portion in which there areprovided four adjacent faces which are parallel to the axis of thecutter, defining four edges of which one is in alignment with a cuttingtooth, the radial cutting teeth preferably being angularly spaced in anirregular manner.

A cutting tool of this kind can be entirely produced by milling so thatthere is no difficulty in producing the tool, while the alignmentbetween an edge provided on the shank portion and a cutting toothaffords the advantage of forming a marker means for setting the cutterin place on a sharpener.

A tool assembly which in combination comprises the above-describedarrangements (rigid fixing on a tap body, a guiding action in threevertically displaced regions of the tool carrier shaft, axial fixing ofthe tool carrier shaft without play with respect to the guide, and atool with suitably distributed cutting teeth) makes it possible tomachine a tap seat by grinding, with an absolutely perfect finish.

Other features and advantages of the invention will be apparent from thefollowing description which is given by way of example with reference tothe accompanying drawings in which:

FIG. 1 is an elevational view in cross-section of a tool assemblyaccording to the invention, for repairing a tap seat by grinding theseat;

FIG. 2 shows a perspective view of an accessory which can be used incertain particular cases;

FIGS. 3 and 4 show views on an enlarged scale and by way of example ofpart of a screwthread on an end portion, in accordance with theinvention, which is engaged into two nuts of different types,

FIG. 5 shows a view on an even larger scale than the views of FIGS. 3and 4 of a portion of screwthread in accordance with the invention,which is engaged in two nuts of different types,

FIGS. 6 and 7 are a perspective view and a cross-sectional viewrespectively of an alternative form of a tool assembly according to theinvention,

FIG. 8 is an elevational view of a cutting tool,

FIG. 9 is a view of the cutting tool of FIG. 8 as viewed in thedirection indicated by arrow F in FIG. 8, and

FIGS. 10 and 11 are views similar to those of FIGS. 8 and 9, of analternative embodiment.

In the selected embodiment shown in FIG. 1, the tool assembly forrepairing a tap seat by grinding thereof comprises a guide 300associated with an adapter which is indicated generally at 301 and whichcomprises an end portion 302 on which a casing member 303 is mounted.The end portion 302 preferably has a V-section screwthread whosecharacteristics will be set forth hereinafter, and a support bearingsurface 305 which is intended to co-operate with a terminal face 306 inthe tap body 307, the tap body being shown partly in phantom.

The guide 300 is associated with the casing member 303 by screwing andfor this purpose it comprises a screwthread 310 adapted to co-operatewith a fixing and forward feed screwthread 311 provided in the top partof the casing member, which moreover in its bottom part is associatedwith the end portion by screwing, alignment between the components 302and 303 being ensured by a tapered bearing surface 312.

The tool carrier shaft 315 is axially fixed with respect to the guide300 by means of a thrust bearing.

In accordance with the invention, the thrust bearing comprises aball-bearing thrust means generally indicated at 316. The inner race orcage 317 of the ball-bearing thrust means is fixed with respect to thetool carrier shaft by means of a shoulder 318 provided on the shaft, anda clamping nut 319, while the outer cage or race 320 is fixed withrespect to the guide 300 by bearing on a ring 321 which is inserted in acircular groove 322 provided in the guide, and by a ring 323 with anexternal screwthread.

In accordance with a particular feature of the ball-bearing thrustmeans, the roller tracks provided in each cage or race are formed bygrooves 324 whose depth is such that the balls 325 are enclosed over themajor part of their surface area; in other words, there is an extremelysmall clearance between the inner and outer races of the ball-bearingassembly.

In accordance with another particular feature of the ball-bearing thrustmeans in question, the grooves 324 comprise edges which do not have anysharp angles, being for example chamferred, rounded, or even better, adivergent region starting from the groove bottom, so that when asubstantial axial thrust force is applied to a race, the thrust forcedoes not mark the balls.

An important advantage which results from such an arrangement is thatthe ball-bearing thrust means, referred to as a double-acting thrustmeans, is capable of absorbing substantial axial forces, both thrustforces and traction forces, for example when the tool assembly is usedbadly, such as forcibly screwing the end portion 302 on to a tap body,with the axial position of the tool carrier shaft causing the tool tobutt against the tap seat to be ground.

As regards radial guiding of the tool carrier shaft 315, in accordancewith a preferred embodiment, the present invention provides anintermediate guide region in the casing member 303, a lower guide regionin the end portion 302, and an upper guide region by virtue of theabove-mentioned ball-bearing thrust means 316.

For this purpose, the casing member 303 and the end portion 302 arebored over their entire length to the same diameter D and D1 so thateach can receive a ring 330 and 331 of anti-friction metal, for examplebronze, which are forcibly fitted into position by means of a press.

The ring 330 is engaged into the end portion by way of the end which istowards the tap body, while as regards the casing member 303, the ring331 is fitted into place by way of the end at which it is connected tothe guide.

After this operation, the adapter 301 is formed by assembling the endportion 302 to the casing member 303, and the rings are then reamed orbroached so as to provide perfect alignment thereon.

Another ring 332 of felt or the like, which is impregnated with oil, istightly fitted into the bore D1 of the casing member, more particularly,in the space between the casing member and the end portion; a secondring similar to the above-mentioned ring 332 could also be fitted intothe bore D in the end portion 302 above the anti-friction ring 330.

Two diametrically opposed marking means 334 are provided on the outsidesurface of the guide in order to check the axial movement of the toolcarrier relative to the adapter, the marking means in the embodimentillustrated being produced by punching or drilling.

At the end remote from the tool, the tool carrier shaft 315 is providedwith an operating wheel which has an oblong portion 350A adapted tofacilitate gripping thereof, in order to carry out the grindingoperation proper, the portion 350A itself being extended by acylindrical portion 350B which is arranged to permit rapid rotary driveof the tool carrier, for the finishing operation.

It should be noted that in some cases, the tap seat is disposed withinthe tap body at a depth such that the maximum axial movement of the toolcarrier of the above-described tool does not make it possible to repairthe seat. So that such seats can be ground in accordance with thedescribed method, the present invention provides supplementing the toolassembly by an accessory component which forms an extension member, asshown in FIG. 2.

Referring to FIG. 2, the extension member is drawn from a six-sided barand then machined so as to have a cylindrical portion of revolution 340followed by a screwthread 341 adapted to receive the cutting tool.Internally, the extension member comprises a chamber 342 of the samediameter as the tool carrier 315, extended by a screwthread 343 adaptedto receive the threaded end 315A of the tool carrier which normallycarries the tool, a support bearing surface 344 being provided betweenthe chamber 342 and the screwthread 343.

In combination with the above-described arrangements, the end portion302 comprises a screwthread with at least one turn but preferably twoturns, whose pitch is intermediate the pitches of two different types ofa range of types of tap body nuts or female screwthreads.

A screwthread of this kind on an end portion of a tool assembly is shownon a larger scale in FIGS. 3, 4 and 5.

Referring now to FIGS. 3, 4 and 5, the end portion screwthread isindicated generally by V, while two different types in a range of typesof tap body nuts are indicated by E and E1; P denotes the pitch of thescrewthread on the end portion; P1 denotes the pitch of the nut E, P2denotes the pitch of the nut E1; D denotes the diameter of thescrewthread at the crests or tops of the turns; D1 denotes the diameterof the screwthread at the screwthread bottom; H denotes the height ofthe turns; A denotes the thickness of a turn at the base thereof and A1denotes the distance between two turns.

In the embodiment illustrated, the diameter of the nuts E and E1 is 20mm, the pitch of the nut E1 being 1.25 mm while the pitch of the nut Eis 1.50 mm.

An end portion screwthread which is intended to be screwed on to eitherone of the two nuts indicated above comprises at least one turn butpreferably two turns, as indicated at S and S1, on respective sides ofwhich are provided on the one hand a relief portion 355 of constantheight and on the other hand a cylindrical terminal portion ofrevolution 356.

The portion 355 is delimited by a bearing shoulder 357.

The end portion screwthread in the embodiment illustrated has anintermediate pitch P of 1.411 mm; it has a height H of 0.75 mm, adiameter D of 19.80 mm and a diameter D1 of 18.30 mm; the thickness A ofthe turns is 0.92 mm and the distance A1 between the two turns is 0.491mm.

As can be clearly seen in particular in FIG. 5, the diameter D1 at thebottom of the thread formed by the turns is adapted to the smallest ofthe screwthread crest diameters of the two types of nut E and E1selected.

Moreover, the reduced-thickness profile of the turns provides, withrespect to one or other of the profiles of the nuts, a supplementaryclearance J which is additional to the initial clearance which isnormally provided between the male and female threads, so that theclearance between said components is at least equal to half thedifference between the two pitches.

The groove 355 provided between the shoulder 306 of the adapter and thefirst turn S is of a diameter which is preferably equal to the bottom ofthe screwthread of the end portion, while the groove 355 is of a uniformheight Y.

When the end portion 302 is screwed into a nut or female thread, andwhen the shoulder 306 on the end portion butts against the terminal faceof the tap body 307, the tool assembly is fixed to the tap body by thecontact of at least one portion of a thread turn with a side of thefemale screwthread.

In FIG. 3, the V-shaped screwthread on the end portion is screwed intothe nut or female member E having a pitch of 1.5 mm, and it is part ofthe side F of the turn S1 which is in contact with a portion of the sideof the screwthread as indicated at F1 of the nut or female member.

In FIG. 4, the V-shaped screwthread of the end portion is screwed intothe nut or female member E1 having a pitch of 1.25 mm, and contactbetween the male thread and the female thread is established by the twoturns of the end portion screwthread, respectively by a portion of theside F of the turn S and by a portion of the side F' of the turn S1.

Thus, the end portion screwthread, by virtue of its intermediate pitch,permits the tool assembly to be satisfactorily fixed on two types of tapbody nuts or female threaded members.

The following table shows by way of example the characteristics of endportion screwthreads V according to the invention, for a range of nutsor female threaded members E.

                  TABLE                                                           ______________________________________                                        NUTS (E)             SCREWS (V)                                               φ                                                                             P1     P2      PITCH   H    A    A1   D     D1                            ______________________________________                                        16  1.5    1.25    1.411   0.75 0.92 0.491                                                                              15.80 14.80                         17  1.5    1.337   1.411   0.83 1.07 0.341                                                                              16.60 14.94                         3/8                                                                           18  1.5    1.25    1.411   0.75 0.92 0.491                                                                              17.80 16.30                         19  1.5    1.25    1.411   0.75 0.92 0.491                                                                              18.80 17.30                         20  1.5    1.25    1.411   0.75 0.92 0.491                                                                              19.80 18.30                         21  1.814  1.5     1.65    1.09 1.37 0.28 20.80 18.62                         1/2                                                                           22  1.5    1.25    1.411   0.75 0.92 0.491                                                                              21.80 20.30                         23  1.5    1.25    1.411   0.75 0.92 0.491                                                                              22.80 21.30                         26  1.814  1.5     1.5     0.93 1.22 0.28 25.96 24.10                         3/4                                                                           ______________________________________                                    

Reference will now be made to FIGS. 6 and 7 which show an alternativeform of a tool assembly according to the invention.

In this embodiment, the tool assembly comprises a guide 400 in the formof a sleeve associated with an adapter which is indicated generally at401 and which comprises, on respective sides of the tightening wheel401A, an end portion 401B and a casing portion 401C.

The end portion with a screwthread V, the casing portion and thetightening wheel form a unitary adapter which is produced by moulding asuitable plastics material.

The casing portion 401C carries the guide 400 with which it isassociated by a male thread-female thread system; for this purpose, thecasing portion 401C comprises, over its entire height, a fixing andforward feed screwthread 401D co-operable with a screw-threaded bore400A in the guide 400.

The guide 400 is also formed by moulding a suitable plastics materialand it comprises a bottom portion 400C in which there is an axialopening 400D. The outside surface of the guide, in order to facilitategripping thereof, comprises grooves which extend along generating lines,but the grooves are interrupted over a circumferential portion indicatedat 400B. The ungrooved region 400B, which is advantageously flat, isintended to form a marking means, the purpose of which will becomeapparent hereinafter.

Internally, between the tightening wheel 401A and the free terminal partof the end portion 401B, the adapter comprises an axial passage 401Ewhich is adapted to provide a guiding action for a tool carrier shaft410 associated with and axially movable in the guide 400.

For this purpose, the tool carrier shaft 410 comprises a shoulder 410Aagainst which bears an anti-friction washer 411 which is trapped betweenthe shoulder 410A and the bottom portion of the guide; on the other sideof the washer 411, the tool carrier shaft comprises a screw-threadedportion 410B on to which a tightening nut 412 and a drive wheel 413 arescrewed.

It should be noted that the nut 412 is adjusted on the screw-threadedportion so as to permit the tool carrier shaft to rotate with axial playwhich is just necessary for such rotary movement, while the wheel 413also forms a lock nut means for locking the nut 412.

The drive wheel on the tool carrier shaft 410 is also of mouldedplastics material; it comprises a base portion 413A which is oblong inshape and on which is provided a cylindrical button portion 413B ofrevolution; vertical grooves 413C and 413D respectively are provided onthe side faces of the portion 413A and on the outside surface of theportion 413B.

The tool assembly is advantageously completed by a cutting tool such ascutters as shown in FIGS. 8 to 11. In FIGS. 8 and 9, the cutter which isindicated generally at 529 is produced from a drawn component and has aterminal cutting face comprising three radial cutting teeth 530 to 532which are disposed at 120° relative to each other, and a shank portionof square cross-section wherein one of the edges 533 is aligned with acutting tooth, in the embodiment illustrated being the tooth 530.

The purpose of aligning the edge 531 with a cutting tooth is to form amachining marker point and to make it possible in particular whensharpening the cutting teeth to deal with the teeth successively in theorder in which they were produced by milling.

An axial screw-threaded opening 535 is provided in the cutter forassembling the cutter to the tool carrier shaft.

In FIGS. 10 and 11, the cutting tool is generally similar to thatdescribed hereinbefore, but the radial cutting teeth have the particularfeature of being arranged with an irregular angular offset relative toeach other, for example an angle of 120° between one tooth 540 and onetooth 541; an angle of 105° between the tooth 541 and a tooth 542; andan angle of 135° between the tooth 542 and the above-mentioned tooth540; for sharpening purposes, the tooth 540 is advantageously marked bymeans of a mark provided at the periphery of the rear portion of thetool.

In this way, only a single tooth at a time engages a precedingimpression so that the force to be applied to the operating wheel todrive the tool in rotation may be applied virtually without effort.

It will be noted that each cutting tooth is extended by a relief portion543 to facilitate release of the cuttings, while an axial screw-threadedbore 540 is provided to permit the tool to be fitted to the toolcarrier.

It will be appreciated that the diameter of the cutting tools and thenumber of teeth may be different from the foregoing description,according to requirements, while being in accordance with the particularfeatures described hereinbefore.

The tool assembly is advantageously completed by a tapered or conicalfinishing cutter with a single tooth (not shown), which is arranged toprovide a chamfer on the edge of the seat, formed by the liquid inletduct, this being in order to prevent damage to the seal on the tap head.

With such a tool assembly, it is necessary to determine thecharacteristics of the nut or female member in which it is to be fixedin order to select an adapter which can be fitted to one or other of thetwo different types of nuts or female members in a range of typesthereof.

For carrying out a grinding operation, the tool assembly is prepared byunscrewing the guide which causes the shaft for carrying the tool to beretracted until the tool is brought into contact with the end portion,as shown in FIG. 7.

The tool assembly can then be fixed to the tap body after the head ofthe tap has been removed.

The cutting tool is brought into contact with the seat to be repaired,by screwing the guide on to the casing member or portion, the screwingaction being stopped as soon as a resistance is felt at the guide.

At this stage, the angular position of the guide is checked by means ofthe marking means, and then the drive wheel for driving the tool carriershaft is rotated in the clockwise direction and, at the same time, theguide is turned, the guide being rotated substantially more slowly thanthe drive wheel.

The rotary movement of the guide will generally be limited to one thirdor two thirds of a turn so that, depending on the pitch of the malethread-female thread system which connects the guide to the casingmember or portion, the axial travel of the tool will correspond toremoving a thickness of metal of from 0.3 to 0.5 mm.

When this operation, referred to as roughing out, is concluded, afinishing operation is performed by rapidly rotating the shaft carryingthe tool by means of the rapid drive button portion, while the guide isrotated over a small angular distance, of the order of 0.5 mm.

While the cutter is still rotating and in order to ensure that it doesnot leave any traces on the tap seat, the guide is rapidly rotated in ananti-clockwise direction, the grinding operation thus being completed sothat the tool assembly can be disconnected from the tap body.

After checking the seat, a cleaning operation will be effected, by meansof rinsing, in order to remove the cuttings.

It will be appreciated that tap heads may comprise a screwthread ofintermediate pitch in accordance with the invention, so that the sametap head could be fixed on to one or other of two tap bodies comprisinga female thread of different pitch, the main advantage of such anapplication of the invention being to limit the stocks of tap headssubstantially to half, hence giving a substantial saving in space and asubstantial financial saving.

It will be appreciated that the invention is not limited to the selectedembodiments illustrated in the drawings which on the contrary may bemodified without thereby departing from the scope of the presentinvention. Thus, in a possible alternative embodiment, the nut 412,FIGS. 6 and 7, could be omitted by causing the end of the screw-threadedportion 410B of the tool carrier shaft to butt against the bottom of thescrew-threaded bore in the wheel 413, while the wheel 413 would beadapted to rest on the upper end face of the guide 400, leaving theminimum clearance required for rotation thereof.

Likewise, in another alternative form, the wheel 413 of the tool carriershaft could be moulded on to the portion 410B of the tool carrier shaft.

I claim:
 1. A tool assembly for repairing and in particular grinding atap seat, comprising a cutting tool carrier shaft, a guide carrying saidshaft and an adapter carrying said guide, the adapter having an endportion forming a replica of the tap head normally associated with thetap body, with a screwthread which is complementary to that of said tapbody, said end portion having mounted thereon a casing member comprisinga screwthread for fixing and forwardly moving the guide, comprising askirt portion with, at a terminal part, a thrust bearing for the toolcarrier shaft, and having in its interior a screwthread capable ofco-operating with said fixing and forward feed screwthread, the toolcarrier shaft extending beyond the bearing to the operating meansprovided at its free end, characterised in that the thrust bearingcomprises a double-acting ball-bearing thrust means whose outer race isfixed with respect to the guide while the inner race is fixed withrespect to the tool carrier shaft which is arranged for that purpose,thereby to provide for axial fixing without play of the tool carriershaft with respect to the guide, and further characterised in that atthe same time the radial guiding action in respect of the tool carriershaft is provided by means of at least one anti-friction ring which isbroached after being force-fitted into one or other of the endportion-casing member components.
 2. A tool assembly according to claim1 characterised in that the radial guiding action in respect of the toolis provided by two broached rings of anti-friction metal such as bronze,one ring being force-fitted in the end portion at the end towards theconnection to the body of the tap, and the other also being force-fittedinto the casing member at the guide end, said rings being broachedjointly.
 3. A tool assembly to claim 1 or 2 characterised in that thecasing member carries a felt ring around a portion of the tool carriershaft, said ring being impregnated with a lubricant.
 4. A tool assemblyaccording to claim 1 characterised in that the races of the ball-bearingthrust means comprise deep grooves arranged to enclose at least half thecircumference of the great circle of the balls in such a way that theresulting bearing is capable of carrying substantial longitudinal forcesif such occur.
 5. A tool assembly according to claim 4 characterised inthat the inner ring is fixed with respect to the tool carrier shaftbetween a circular support shoulder provided in the shaft and a clampingnut which is screwed on to said shaft, while the outer ring is fixedwith respect to the guide between a support means provided in the guide,and a nut screwed thereinto.
 6. A tool assembly according to claim 1characterised by:an end portion screwthread comprising at least one turnwhich is of a pitch intermediate the pitches of two different types of arange of types of tap body nuts or female members; a thread bottomdiameter which is adapted to the smallest of the thread crest diametersof the two types of nuts; a reduced-thickness thread profile whichprovides with respect to one or other of the nut profiles of the twotypes, a supplementary clearance which is at least equal to half thedifference between the two pitches.
 7. A tool assembly according toclaim 1 characterised in that the cutting tool is a milling cuttercomprising a terminal cutting face having three radial teeth disposed atangles of 120° with respect to each other, and a shank portion of squarecross-section, one of the apexes of the square being aligned with acutting tooth.
 8. A tool assembly according to claim 7 characterised inthat the radial cutting teeth are distributed at an irregular angulardisplacement relative to each other.
 9. A tool assembly according toclaim 8 characterised in that the angular displacement of the teethrelative to each other is as follows: between a first tooth and a secondtooth an angle of 120°, between said second tooth and a third tooth anangle of 105°, and finally an angle of 135° between said third tooth andsaid first tooth, said first tooth also being disposed in alignment witha marking means previously provided on the periphery of the cutter. 10.A tool assembly according to claim 1 characterised in that the adapteris an integral component, and comprises a casing portion which isintended to be screwed to the guide, an end portion having ascrewthread, and, between said casing portion and said screwthread amanual clamping wheel.
 11. A tool assembly according to claim 1characterised in that the guide is provided on its outside surface withat least one means for marking the forward movement of the guide, formedby a flat portion extending along a generating line, or formed by atleast one punching.
 12. A tool assembly according to claim 1characterised in that the guide, the adapter and the actuating meansformed by a wheel member for driving the tool carrier shaft are moulded,preferably of plastics material.
 13. A tool assembly according to claim12 characterised in that the wheel member is fixed to the tool carriershaft, said wheel means comprising an oblong portion with a rapid driveknob portion disposed thereon.
 14. A tool assembly according to claim 12characterised in that the guide carries the tool carrier shaft on theone hand by means of a nut bearing against a bottom portion of the guideand screwed on to a screw-threaded portion provided for that purpose ofsaid shaft, and on the other hand by means of a friction washer trappedbetween the inner face of said bottom portion of the guide and ashoulder provided in the tool carrier shaft, which nut can benon-rotatably locked by means of a lock nut means.
 15. A tool assemblyaccording to claim 14 characterised in that the lock nut means comprisesthe wheel member for driving the tool carrier shaft.
 16. A tool assemblyaccording to claim 12 characterised in that the wheel member for drivingthe tool carrier shaft comprises a screwthread adapted to form anabutment means at the end of a screw-threaded portion of the toolcarrier shaft, and is adapted to bear against the upper end face of theguide with a minimum clearance necessary for rotation thereof.
 17. Atool assembly according to claim 12 characterised in that the toolcarrier shaft drive wheel member is moulded on to a screw-threadedportion of the tool carrier shaft.